Numerous studies suggest that the in vivo metabolism of benzo(a)pyrene (BP) and other carcinogens is altered when animals are pretreated with anticarcinogenic agents such as butylated hydroxy anisole (BHA). Based on these observations, we have initiated studies to determine the type and amount of in vivo metabolic alteration and DNA binding of BP in animals pretreated with BHA. At present, the profiles of the glucuronide and sulfate conjugates in the bile have been determined in control and BHA treated animals. No sulfate conjugates were detectable in control or treated animals. Glucuronide conjugation accounted for 30% of the dose in control and treated animals - BHA pretreatment altered the profile of the glucuronide metabolites. The amount of 6-hydroxy BP was decreased in BHA treated animals and the amount of 4,5-dihydrodiol BP was concomitantly increased. This could have implications as to the anti-carcinogenic action of BHA since 6-hydroxy-BP has been suggested to be a carcinogenic metabolite of BP. Recycled metabolites of BP were also decreased by BHA pretreatment.